1. Field of the Invention
The present invention relates a method of controlling a semiconductor laser.
2. Description of the Related Art
A wavelength tunable semiconductor laser is one of optical devices. The wavelength tunable semiconductor laser has a gain for a laser oscillation and selects wavelength. There is a method of tuning wavelength characteristics of loss, reflection or gain by tuning refractive index of an optical functional region such as a diffractive grating provided in an optical waveguide in a resonator, as a method of selecting wavelength.
The method of tuning the refractive index does not need a mechanical movable portion, being different from a method of tuning a mechanical angle or a mechanical length. Therefore, the method has an advantage in reliability and a manufacturing cost. There is a method of tuning a temperature of an optical waveguide, a method of tuning a carrier density in an optical waveguide with current injection or the like, as a method of tuning refractive index of an optical waveguide. There is proposed a semiconductor laser having a Sampled Grating Distributed Bragg Reflector (SG-DBR) in which peak wavelength of reflection peak ranges periodically and a Sampled Grating Distributed Feedback (SG-DFB) in which peak wavelength of gain spectrum ranges periodically, as a concrete example of a wavelength tunable laser adopting a method of tuning a temperature of an optical waveguide.
This semiconductor laser controls a correlation between the reflection spectrums of the SG-DBR and the SG-DFB, selects a wavelength with a venire effect, and emits a laser light. That is, the semiconductor laser oscillates at one of wavelengths where two spectrums are overlapped and reflection intensity gets biggest. It is therefore possible to control the oscillation wavelength by controlling the correlation of two reflection spectrums.
Japanese Patent Application Publication No. 9-92934 (hereinafter referred to as Document 1) discloses a semiconductor laser controlling an oscillation wavelength with a control of refractive index of an optical waveguide. In Document 1, a peltiert device (a temperature control device) and a heater are adopted as a control portion for controlling the refractive index of the optical waveguide. The wavelength is controlled with a control of a temperature control of the optical waveguide with use of the temperature control device and the heater.
However, changing amounts of the two spectrums may differ from each other when the temperature control device controls the temperature of the semiconductor laser. In this case, a desirable oscillation wavelength may not be obtained.